This application corresponds to Japanese Patent Application No. 10-60582, filed on Feb. 24, 1998, which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a method and apparatus for assuring a contact between a measuring terminal and an external electrode of an electronic component in the inspection of characteristics of the electronic component.
2. Description of the Related Art
In the measurement of insulation resistance of capacitors, a measuring voltage is applied to a capacitor and a leakage current of the capacitor is measured after it has been fully charged. A good capacitor naturally exhibits a low leakage current. However, low leakage current occurs even when no adequate contact is established between a measuring terminal and an external electrode of the capacitor. For this reason, the measuring terminal needs to firmly contact the external electrode. However, an oxide or an organic material occasionally forms an insulation layer on the surfaces of the measuring terminal and the external electrode, impeding electrical conduction between the measuring terminal and the external electrode.
The following methods are conventionally used in combination to resolve the problem caused by the presence of the insulation layer.
1) The measuring terminal is wedge-shaped to break the insulation layer of the external electrode of the electronic component.
2) The pressure of the measuring terminal against the electronic component is increased to dent (e.g., dig into) the surface of the external electrode of the electronic component for good contact.
3) When applied, the measuring terminal scrapes the surface of the external electrode of the electronic component to remove the insulation layer on the surface of the measuring terminal and the external electrode of the electronic component.
Since the above methods mechanically establish contact, the following problems arise.
1) Noticeable marks remain on the external electrode of the electronic component, and degrade solderability of the electronic component when it is used.
2) The measuring terminal suffers severe wear, needing frequent replacement and repair.
3) Chip-type electronic components are being produced with smaller dimensions. Accordingly, these small components have small external electrodes. The contact area of these small electrodes with the measuring terminal may not be sufficient, and thereby may fail to provide a good contact.
Accordingly, it is an object of the present invention to provide an inspection method and inspection apparatus for assuring a contact between a measuring terminal and an external electrode of an electronic component (e.g., a discrete electronic component) in the inspection of characteristics of the electronic component.
According to a first aspect of the present invention, an inspection method provides for the inspection of the characteristics of a discrete electronic component by pressing measuring terminals into contact with external electrodes of the discrete electronic component, and then feeding a measurement signal via the measuring terminals. The method includes a first step for applying an electrical signal that breaks down insulation layers of the measuring terminals and the external electrodes, with the measuring terminals pressed into contact with the external electrode. The method also includes a second step for inspecting the characteristics of the discrete electronic component by permitting a measurement signal to flow with the measuring terminals remaining in contact with the external electrodes.
When the measuring terminals are pressed into contact with the external electrodes of the electronic component with a preset electrical signal applied between the measuring terminals, the insulation layers of the measuring terminals and the external electrodes are broken down. The insulation breakdown cleans the insulation layer therefrom, and reduces the contact resistance between the measuring terminals and the external electrodes, reliably establishing the conduction therebetween. Subsequent to the cleaning of the insulation layer, the measurement signal is applied between the measuring terminals with the measuring terminals pressed into contact with the external electrodes, and a signal flowing through the electronic component is detected to inspect the characteristics of the electronic component. In this way, a contact is established between the measuring terminals and the external electrodes without using a mechanical method, and the characteristics of the electronic component are accurately inspected. Since there is no need for pressing the measuring terminals against the external electrode at an unnecessarily strong force, the inspection method works on even a miniature electronic component having a small-area external electrode.
The level of the electrical signal capable of breaking down the insulation depends on the composition and thickness of the insulation layer, but, generally speaking, the application of voltage within a range of 20-10000 V/xcexcm is sufficient to cause insulation breakdown. The electrical signal may be a direct current or an alternating current, or a combination of both (alternating current superimposed on direct current) may be used to establish a reliable contact. The electrical signal may be applied continuously or intermittently.
Preferably, in the first step, two measuring terminals are pressed into each of the external electrodes of the electronic component to apply the electrical signal between the two measuring terminals that remain in contact with the external electrode. (For an electronic component having a pair of external electrodes, the application of the electrical signal, capable of breaking down the insulation, between the external electrodes causes a current to flow through the electronic component itself, possibly adversely affecting its electrical characteristics.) If the electrical signal is applied to the same external electrode, no electrical signal flows through the electronic component itself. For this reason, the insulation layer is broken down regardless of the kind of the electronic component.
Preferably, in the first step, the contact between the measuring terminals and the external electrodes is sensed based on the current flowing between the measuring terminals and the external electrodes when the insulation layer is broken. In this case, contact improvement and contact sensing are performed at the same time. The operation efficiency in inspection is thus increased.
According to a second aspect of the present invention, an inspection apparatus provides inspection of the characteristics of a discrete electronic component by pressing measuring terminals into contact with external electrodes of the discrete electronic component and then by feeding a measurement signal via the measuring terminals. The apparatus comprises an insulation breaking circuit for applying an electrical signal to the measuring terminals that breaks down insulation layers of the measuring terminals and the external electrodes, a measuring circuit for measuring the characteristics of the electronic component based on a signal that flows through the electronic component when a measurement signal is applied between the measuring terminals, and switching means for selectively connecting the measuring terminals to either the insulation breaking circuit or the measuring circuit.
Preferably, the inspection apparatus includes two measuring terminals that are pressed into contact with each of the external electrodes of the electronic component, wherein the insulation breaking circuit applies the electrical signal between the two measuring terminals that remain in contact with the same external electrode.
Preferably, the inspection apparatus includes a contact sensing circuit for sensing a contact between the measuring terminals and the external electrodes, based on a current flowing through the insulation breaking circuit. The inspection apparatus performs the contact improvement and contact sensing at the same time.